[clang-tools-extra] Add --project-root to clangd (PR #155905)

[Nathan Ridge via cfe-commits]

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@@ -500,6 +500,16 @@ opt<bool> EnableConfig{
     init(true),
 };
 
+opt<bool> StrongWorkspaceMode{
+    "strong-workspace-mode",
+    cat(Features),
+    desc("An alternate mode of operation for clangd, operating more closely to "
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HighCommander4 wrote:

Suggested reword: "operating more closely to the workspace" --> "where the clangd instance is used to edit a single workspace".

https://github.com/llvm/llvm-project/pull/155905